Linear ethylene polymers, particularly linear low density polyethylene (LLDPE) are widely used commercially in films. The films are conventionally prepared by blow film extrusion and have generally good properties but often exhibit undesirably low stiffness for some uses and have marginal machine direction tear and puncture tear propagation characteristics. U.S. Pat. No. 4,579,912, which is incorporated by reference, discloses the use of polystyrene or poly(para-methylstyrene) to improve tear strength and stiffness. It was also found that the addition of polystyrene resin also improved the blocking characteristics and reduced the splittiness as measured by machine direction puncture propagation of the film making it particularly suitable for bags and the like. Later, as disclosed in my U.S. application Ser. No. 902,718, filed Sept. 02, 1986, now U.S. Pat. No. 4,743,649, which is incorporated herein by reference, I discovered that high impact polystyrene (HIPS) gave unexpectedly better anti-blocking properties than crystal polystyrene when added in small amounts to linear ehtylene polymers such as LLDPE.
This invention is based on the observation that better balance of blocking characteristics and other film properties than obtained with polystyrene addition of impact polymer (HIPS) addition can be achieved using both polystyrene and an impact polystyrene or impact poly(para-methylstyrene) resin.